Crustal-scale seismic wave equation modeling demonstrates that wavelength-scale
velocity fluctuations can dominate the seismic response over a wide
range of offsets and that a wide range of velocity distributions
qualitatively can explain deep seismic data. This range can be narrowed
by studying the detailed petrophysical and structural properties
of middle and lower crustal exposures. The Ivrea Zone, in the Southern
Alps, is a well-studied sliver of extended lower continental crust
brought into its present upright position as a result of late Alpine
lithospheric shortening. The high degree of structural and petrophysical
complexity and in particular the limited exposure of the Ivrea Zone
favor a statistical rather than deterministic approach to develop
a two-dimensional crustal-scale seismic model. For this purpose we
digitized two 1:25,000 geological maps from the central Ivrea Zone
on a 60-m grid. We find that the Ivrea Zone is characterized by a
bimodal velocity distribution, and a band-limited self-affine structure
having a fractal dimension of 2.7, a characteristic horizontal scale
of 500 to 1000 m, and an aspect ratio around 4.0. Assuming statistical
stationarity, a realization of this stochastic model was used to
develop synthetic seismograms typical of ''Ivrea-type'' lower continental
crust. Our results indicate that (1) Ivrea-type lower crust can explain
qualitatively commonly observed lower crustal reflectivity, (2) relatively
minor changes in bulk composition and/or metamorphic grade may lead
to dramatic changes in reflectivity, which cannot be explained by
current generic models on the origin of lower crustal reflections,
and (3) travel time interpretation of the synthetic wide-angle data
may lead to erroneous large-scale velocity structures.